1. Field of the Invention
This invention relates generally to a sensor mechanism and, more particularly, to a compact low paper sensor mechanism.
2. Description of the Background
Presently, there are several different types of printers available. However, all printers share common components, such as a print head, a platen, a paper supply and a control mechanism. The control mechanism controls a motion of the print head relative to the paper supply, selects a character to be printed, and advances and retracts the paper supply, as necessary.
However, regardless of the type of printer used, it is generally undesirable to operate a printer without paper. For example, ink-based printers that are operated without paper will transfer ink into the platen, which may, in turn, stain a back side of subsequent sheets of paper and may also damage print writes within the print head.
Also, thermal printers that are operated without paper may overheat, since the paper is also used to absorb heat generated by the print head during printing operations. In addition, operating thermal printers without paper may cause excessive wear to the print head, since the print head would be running directly on the platen, instead of on the paper.
Therefore, in order to avoid operating the printers without paper, conventional printers have been provided with low-paper sensing and warning systems. Moreover, low-paper sensing has recently become an important requirement, as retailers move towards system management, which requires system notification that a paper supply is near completion.
However, previously developed low-paper sensors have poor accuracy. That is, since these low-paper sensors typically consist of a lever that rubs on one side edge of a paper supply roll, the lever either drops over the top of the paper supply roll or into a core of the paper supply roll due to a movement (e.g., bouncing or jumping) of the paper supply roll during an operation of the printer; thereby causing the lever to erroneously trip a switch to indicate that the paper supply is low.
Therefore, in order to address the poor accuracy of these low-paper sensors, printers have been provided with a sensing mechanism that includes an optical sensor and two support rollers, which support a paper supply roll. The two support rollers are spaced apart from each other at a predetermined distance, so that when a diameter of the paper supply roll becomes less than the predetermined distance, the paper supply roll drops between the two rollers and is then detected by the optical sensor. However, printers with such a sensing mechanism require an additional amount of space in order to accommodate for the paper supply roll which is allowed to drop between the two rollers, which, in turn, increases a size and a manufacturing cost of the printer.
Thus, what is needed is a sensor mechanism capable of accurately detecting a low paper condition while minimizing a required space within a printer.